Recently, with the dramatically increasing demands of portable electronic products such as laptop computers, video cameras, mobile phones, and the like, and competitive development of electric vehicles, storage batteries for energy storage, robots, satellite, and the like, studies are actively being conducted on high performance secondary batteries that can be recharged and used repeatedly.
Currently, available secondary batteries include nickel-cadmium batteries, nickel-hydrogen batteries, nickel-zinc batteries, lithium secondary batteries, and the like, and among them, lithium secondary batteries are gaining attention due to advantages of charging and discharging freely in the absence of a memory effect, a very low self-discharge rate, and a high energy density when compared to nickel-based secondary batteries.
On the other hand, with the approaching exhaustion of carbon energy and growing interests in environment, the demands for hybrid vehicles and electric vehicles are gradually increasing all over the world including U.S.A., Europe, Japan, and Korea. The hybrid vehicles and electric vehicles are supplied with power and can travel using charging and discharging energy of a battery pack, and thus have good reputation from many consumers in that they have high fuel efficiency and create little or no pollutant emissions, in comparison to vehicles using only engine. Thus, more interests and studies are focusing on an automotive battery essential to hybrid vehicles or electric vehicles.
FIG. 1 is an exploded perspective view schematically illustrating a configuration of a battery pack according to a related art. Referring to FIG. 1, the battery pack 10 according to the related art includes a pouch-type secondary battery 12, a protection circuit 13, a label film 14, and a frame 11.
The pouch-type secondary battery 12 is manufactured by heat fusion of an upper pouch film and a lower pouch film with a cell assembly interposed between the upper pouch film and the lower pouch film, the cell assembly formed by a stacking at least two unit cells, each unit cell including a cathode plate, a separator, and an anode plate. In this instance, because a general pouch film is made based on a thin aluminum metal layer having high ductility, the pouch-type secondary battery 12 has a disadvantage of being more prone to deformation from external impacts or the like, than a cylindrical or prismatic secondary battery.
Accordingly, in the manufacture of the battery pack 10 using the pouch-type secondary battery 12, the battery pack 10 is manufactured in the manner of mounting the pouch-type secondary battery 12 in the frame 11 to protect the cell assembly therein from external impacts or the like, while maintaining the shape of the pouch-type secondary battery 12.
The protection circuit 13 serves to prevent the pouch-type secondary battery 12 from being damaged due to an accident or the like that may occur during operation of the pouch-type secondary battery 12, or protect a user of the battery pack 10 from such accidents.
The frame 11 serves to maintain the outer shape of the pouch-type secondary battery 12, and protect the secondary battery and various circuit devices required for the secondary battery from external impacts or the like. That is, as described in the foregoing, because the pouch-type secondary battery 12 is more prone to deformation than a cylindrical or prismatic secondary battery, the frame 11 surrounding the outer surface of the pouch-type secondary battery 12 is used.
The label film 14 serves to increase the bond strength between the pouch-type secondary battery 12 and the frame 11 and prevent foreign impurities from entering a bonding portion of the pouch-type secondary battery 12 and the frame 11 or from introducing into the frame.
Because the battery pack 10 is primarily used in portable electronic devices, there is a limitation on the size of the battery pack 10. That is, when the battery pack 10 is excessively larger than a housing space of a portable electronic device, it is difficult to install the battery pack 10 in the portable electronic device.
Here, the size of the battery pack 10 is mainly determined by the size of the pouch-type secondary battery 12 and the size of the frame 11. However, it is easy to uniformly manage the standards for the frame 11, while it is not easy to uniformly manage the standards for the battery pack after the frame 11 is surrounded by the label film 14. That is, there is apprehension that the size of the battery pack may change based on a difference in thickness of the label film 14 or an extent to which the label film 14 and the frame 11 are in close contact with each other. As a result, in some instances, there may be difficulty with dimension management of the battery pack.
Additionally, due to an abnormal situation, in the event of occurrence of a phenomenon in which a wing folding part (w) of the secondary battery 12 spreads, the frame 11 surrounding the outer surface of the secondary battery 12 may be deformed. Due to deformation of the frame 11, the overall size of the battery pack increases, making dimension management of the battery pack difficult. A further detailed description will be provided with reference to FIG. 3.
FIG. 2 is a diagram illustrating a deformed state of the wing folding part of the secondary battery according to the related art. That is, FIG. 2 is a diagram illustrating the secondary battery of FIG. 1 when viewed from the rear in FIG. 1 (when viewed in the direction of arrow A).
Referring to FIG. 2, the wing folding part (w) of the pouch-type secondary battery 12 is illustrated as spreading outward. When the pouch-type secondary battery 12 received in the frame 11 is deformed as shown, the side surface of the frame 11 is subjected to outward pressure. Thus, there is apprehension that the frame 11 will spread outward. As a result, the overall size of the battery pack increases, making dimension management difficult.
Moreover, when the pouch-type secondary battery 12 expands due to a swelling phenomenon, the frame 11 may be deformed. Its description will be provided with reference to FIG. 4.
FIG. 3 is a front elevational view in cross section schematically illustrating a deformed state of the battery pack according to the related art.
Referring to FIG. 3, the pouch-type secondary battery 12 received in the frame 11 expands in the lateral direction, and the frame 11 is in a deformed state in the lateral direction. Here, a dotted line (L) surrounding the frame 11 represents a maximum tolerance of the battery pack 10 according to the related art. That is, in the case where the frame 11 is deformed within the range of the dotted line (L) as shown, such deformation is within an allowable dimensional range, but in the case where the frame 11 is deformed beyond the dotted line (L) range departing from the allowable dimensional range, the battery pack 10 is not installed in a portable electronic device, and even if it were so, the battery pack separates from the electronic device and consequently may be easily damaged by the external impacts.
However, studied have focused on the frame 11 based on a function of protecting the secondary battery, while studies about a dimension management function are yet unsatisfactory.